Autotrol 1550-TC is just the way many Autotrol Series 155 Timer Housings are labeled ( 440 timers ). And normally the valve is Model 155. This is the same design used for almost 30 years (replaced by the updated 255 Series in late 1996 ). If you have any doubt - see: Autotrol 155 or 255 - How to Tell Which You Have
